(a) Field of the Invention
The present invention relates to a speed change control structure for an electric tool, and more particularly to a speed change control structure that can prevent actuation of the speed change device caused by inadvertent pressing of a push button or pushing of a push block.
(b) Description of the Prior Art
Speed change control structures are commonly found in all kinds of electric tools. For speed change control structures that are exposed on housing of the electric tools, they are mostly in the form of a single push block or a single press button. When the push block or the press button is embedded in the housing, a speed change device inside the electric tool. During operation, the push block is pushed in a single direction or the press button is pressed to actuate the electric tool. Although the operation thereof is simple and convenient, inadvertent actuation of the electric tool may occur, which lead to accidents. Disadvantages of the prior art can therefore be summed up as follows:
1. As conventional speed change device can be easily actuated by moving the push block or pressing the press button, if the electric tool is disposed in a place to where children have access, accidents may occur. PA1 2. Inadvertent actuation of the speed change control structure that causes the speed of an electric tool to increase may result in sticking of the cutter of electric tool in the workpiece or breaking thereof. If the speed change control structure is inadvertently actuated and the speed of the electric tool as a result increases, the cutter on the electric tool may become stuck in the workpiece or break. For instance, if an electric drill is used to bore holes in a hard workpiece and the torque of the electric drill at high speed is insufficient, it should work at a low speed in order to achieve a greater drilling torque. If the speed change control structure is actuated inadvertently so that the drilling speed is instantly increased, the drill bit may become stuck in the workpiece. Continuous drilling may even result in overheating of the electric drill or breaking of the drill bit. The broken pieces may fly over the place and hurt the operator and people nearby.
3. Inadvertent actuation of the speed change control structure that causes the speed of an electric tool to increase may also result in melting of the workpiece due to high-speed rotation of the cutter. For instance, if an electric saw is used to cut an acrylic board or a board made from petrochemical materials, the cutting speed cannot be excessive. If the speed instantly increases due to inadvertent actuation of the speed change control structure, friction between the saw blade and the workpiece will drastically increase, and the region surrounding the sawed portion will melt due to high heat, and the molten portions will stick to the saw blade and prevent movement of the saw blade. As a result, not only the sawed material will become useless, the electric saw will also be damaged.